The present invention relates to a compatible disk player for playing both a digital audio disk CD (compact disk) and a video disk LD (laser disk).
Generally, a compatible disk player, which is a general term meaning both CD and LD compatible, automatically loads a disk. Within the compatible disk player, the initial playing position of the pick-up relative to the disk will differ between CD and LD systems. Consequently, it is necessary to determine whether the disk to be played is a CD or LD. The disk type is determined by detecting its size, since CD's conform to two smaller diameter disks; namely, 8 cm or 12 cm, while LD's conform to two larger diameter disks; namely, 20 cm or 30 cm.
The methods for determining the disk type by detecting its size include, (1) a determination method using photo sensors and (2) a determination method using a sequence operation.
In the photo sensor method, at least two photo sensors are used for the CD system and the LD system. This combination of sensor outputs can determine three cases, including a CD presence, an LD presence, and the absence of either disk. However, this method results in increasing the production cost, in view of the additional circuitry and sensors.
Alternatively, the sequence operation of the second determination method may be used, as will be described hereafter in reference to the flow chart shown in FIG. 4. Before the disk type is determined a ready position of the pick-up is set wherein the ready position is located radially beyond the outer diameter of the 12 cm CD and radially within the outer diameter of the 20 cm LD. While the pick-up is set in the ready position, a focusing operation is executed (step S41) to determine whether a focusing servo signal is obtained at the ready position (step S42). When the focus servo signal is obtained, it means an LD is mounted in the playing position. Therefore, the pick-up is moved to the initial playing position of the LD (step S43), and the spindle servo control is executed (step S44). The compatible disk player is then ready to play the LD.
Alternatively, if the focus servo signal is not obtained, it means an LD is not mounted. Thereafter, the pick-up is moved to the playing start position of the CD (step S45). In this position, the focusing operation is executed again (step S46) to determine whether the focus servo signal is obtained at the playing start position of the CD (step S47). When the focus servo signal is obtained, it is determined the CD is mounted at the playing position. Therefore, the spindle servo control is executed to shift to a CD play mode (step S48). When the focus servo signal is not obtained, it means the CD is not mounted at the playing position. Then the player determines there is no disk present.
In the second determination method (sequencing operation), whenever the disk is mounted, the aforementioned sequence operation is executed. However, before the CD is played, it is always necessary to check that an LD is not mounted. Thus, a delay results between the time the CD is set on the loading tray and a playback sound is generated. This delay is longer than the start delay of a dedicated CD player. As an example, in order to play the CD, assuming that it takes 4 seconds to load and clamp the disk, 2 seconds for the first focusing operation (step S41), 2 seconds for the moving operation of the pick-up to the CD playing start position (step S45), 2 seconds for the second focusing operation (step S46), and 2 seconds for the spindle servo control operation (step S48). Thus, a total of 12 seconds is required from the loading operation to beginning the CD reproduction.
Generally, an LD and CD are not always alternately played. In other words, the user who plays a CD is more likely to play another CD as opposed to an LD. Thus, the 12 sec. time delay between loading and playing each CD is inconvenient for the user.